<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <title></title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        html,body{
            width: 100%;
            height: 100%;
        }
        .main{
            width: 100%;
            height: 100%;
            overflow: hidden;
            position: relative;
        }
        img{
            width: 100%;
            height: 100%;
        }
        p{
            position: absolute;
            top:20px;
            right: 30px;
            color: white;
            font-size: 20px;
        }
    </style>
</head>
<body>
    <div class="main">
        <img src="/data/upload/mobile/app/05537931961174011.png" alt="">
        <p>3</p>
    </div>
    <script>
        var p=document.getElementsByTagName('p')[0];
        var time=Number(p.innerHTML);
            timer=setInterval(function () {
                p.innerHTML=time--
            },1000)
    </script>
</body>
</html>